Sintered ceramic compositions composed primarily of non-metallic refractory materials have proven advantageous where high temperature resistance, breakage strength, good wear and allied properties are required. Typical instances of use include construction materials and machining tools.
Many such compositions are predicated upon a predominant base material which is aluminum oxide (Al.sub.2 O.sub.3). Aluminum oxide is both abundant and imbued with many of the properties desired for these uses. Unfortunately, it also possesses various deficiencies, such as brittleness. As a result, it has frequently been alloyed with other components in an effort to improve over-all ceramic properties.
Among the other sinterable and machanically resistant materials known to be suitable for this same purpose are many metal carbides, nitrides, borides and other oxides. Some of these materials have been used with aluminum oxide to produce composite compositions having hybrid properties.
A standard of the cutting tool industry, for example, involves aluminum oxide-titanium carbide compositions. These ceramics offer many more desirable physical properties. Unfortunately, they can generally be produced only by hot-pressing procedures. This drawback has contributed substantially to the search for other, less difficult to produce, compositions.
Aluminum oxide-based compositions containing zirconium oxide are also known. In German Offenlegungsschrift No. 2,549,652, it is indicated that aluminum and zirconium oxide compositions, in which the zirconium oxide was transformed from tetragonal to the less dense monoclinic form to create microfissures in the ultimate ceramic article, are desirable. The microfissures are said to increase fracture resistance by allowing absorption of physical stress.
In U.S. Pat. No. 4,218,253, another such composition is described. There, particles of tetragonal zirconium oxide are incorporated within a base material containing aluminum oxide. Instead of possessing microfissures to enhance fracture resistance, however, the resultant ceramic composition is said to improve binding strength by an ability to undergo stress-induced plastic deformation involving conversion of the zirconium oxide to monoclinic form or phase.
Ceramic compositions containing aluminum oxide, titanium nitride and tungsten carbide are also known. In U.S. Pat. No. 4,204,873 such a composition is disclosed, but said composition can be produced only by hot-pressing. U.S. Pat. No. 3,652,304 discloses other nitride-oxide refractories which are produced by hot-pressing.
Notwithstanding the properties of the foregoing compositions, further improvement remains desirable. In many instances, the improvement in the properties has been accompanied by impairment of others. Enhancement of properties without such a drawback therefore remains a highly desirable object.
Improvement in production techniques has also been desired. Most such compositions can be manufactured only by such complicated techniques as hot-pressing. This drawback greatly increases their price.